Cable television systems utilize a central provider of program information which services a large number of end users generally referred to as subscribers. The central provider portion of the cable television system usually called the "headend" provides a plurality of program information as well as other information to the subscribers via a multiple branch distribution network which may define several tiers of distribution facilities.
In addition to actual programming information, the cable television system is required to carry additional management and operating data provided by the headend to the large number of end users or subscribers. Communication from the headend to the subscribers is generally referred to as "downstream" communication. In some cable television systems referred to as one-way, all information and data is transferred downstream. In other cable television systems referred to as two-way systems, communication is also provided from the various subscribers throughout the network to the headend in what is referred to as "upstream" communication. Examples of subscriber originated upstream information may include program purchasing requests, opinion poll responses, and subscriber terminal status information. Upstream communication in cable television systems is provided using out-of-band communication. Such out-of-band communication uses a separate communication capability outside the standard television broadcast channel and thus is not limited to the vertical blanking interval or other time restraint. Instead, a separate carrier, usually between five and thirty megahertz, is modulated with upstream data at the decoder and transmitted to the headend.
Upstream communications are typically effected using either a contention protocol as disclosed in U.S. Pat. Nos. 4,528,663 and 4,553,161 wherein the subscriber's contend for access to the upstream channel or by providing each subscriber with guaranteed access to a respective relatively small portion of the upstream spectrum. Depending on the type and quantity of usage, one protocol may be more advantageous than the other, or a mixture of both may provide the most effective performance.
It is a general object of the present invention to provide an improved upstream data transmission system for cable television. It is a more particular object of the present invention to provide an improved upstream data transmission system for cable television which is able to respond dynamically to operating changes within the cable television system using headend controlled programmable system parameters.